JPS5973910A - Method and apparatus for resin formed product in metal mold utilizing thermal expansion - Google Patents

Abstract

PURPOSE:To prevent the production of sink by clamping continuously the micro clearance between metal molds under high pressure, just before said both molds forming cavity, reach a desirable cavity shape. CONSTITUTION:The parts forming cavities 6, 6' of metal molds 5, 5' are composed of the metal molds 1, 1 relatively unaffected by thermal expansion and the heat receiving members 3, 3 remarkably expanded and contracted by heating and cooling. The material to be formed is injected into the cavity whose volume has been increased owing to the mutual abutting of the pressure receiving surfaces on the end surfaces of the heat receiving members caused by heating, and after the heat receiving members are cooled, the metal molds 1, 1 are approached mutually, thereby forming the final desirable cavity shape.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for molding a resin molded article in a mold that utilizes thermal expansion, and an apparatus therefor.

The present invention also provides an inner wall of a heat-receiving member that surrounds and is fixed to the opposing surfaces of the respective molds of the fibers and the entire surface of the mold, and that surrounds the entire surface of the mold. A molding die is used in which a cavity is formed and the end face of the heat receiving member connected to the inner wall is formed as a pressure receiving surface, and during a mold clamping operation in which the pressure receiving surfaces of these two molding dies are brought into contact with each other, A heating action and a contradictory cooling action are applied only to the heat-receiving member, and the expansion phenomenon caused by the application of the heating action is transmitted to the mold, and the two heat-receiving members are retracted by the reaction force caused by the joining of all pressure-receiving surfaces. A resin material is injected into the cavity whose volume has increased, and then a cooling effect is applied to the heat-receiving member to cause a contraction phenomenon, which is transmitted to the mold and causes the expanding cavity to contract. , which attempts to produce a high-density injection molded product by applying a pressing action to the entire resin injected into the cavity.

Conventionally, when a synthetic resin molded product is removed from a mold, the molded product is often completed with a shape that is more deformed than desired. This deformation phenomenon and its condition are commonly referred to as "sink marks." This "sink mark" phenomenon is a disadvantageous phenomenon that cannot be avoided in the injection molding process of synthetic resins.
If the molded product is intended to be highly precise, products that are distorted due to sink marks are defective and cannot be used. Furthermore, even if the item does not require precision, if it is an item that requires an aesthetic sense, the effect of the desired effect will be halved by "sink marks."

Therefore, in order to eliminate the "sink mark" phenomenon, we first investigated the cause and found that the most common cause was uneven cooling rate immediately after molding, that is, uneven movement change of each molecule. did.

Next, we began investigating countermeasures, and at present, various methods have been developed and implemented to prevent sink marks, and it appears that the measures to prevent external sink marks have been completed.

One of the typical methods is to calculate in advance the denting phenomenon due to sink marks on the product directly formed by the mold at the locations where the ``sink mark'' phenomenon is expected during molding, add up the amount of denting, and calculate the amount of denting in the finished product. The mold has a concave shape so that it is raised.The predicted concave formation of this mold is based on "intuition".
It is formed by However, if it is possible to form a predicted depression in this mold, it is possible to somehow prevent the depression phenomenon caused by the "sink mark" effect through mold processing. However, depending on the type of product, its shape, or a specific part of the product, it may be necessary to modify the mold side, and in such cases, the material to be injected into the mold may be more sensitive than usual. Currently, these disadvantages are prevented by applying high pressure to increase the density of "sink marks" in areas where they are likely to occur.

However, the above-mentioned "sink mark" countermeasures are sufficient if it is possible to prevent the appearance of "sink marks" on the molded product, but some molded products may be affected by stress during molding. There are some types of molded products that do not like it, and others that dislike non-uniform density of molded products, and the above-mentioned two typical countermeasures against "sink marks" cannot be used for these molded products.

Therefore, the present invention was developed, but the cavity in the mold corresponds to the desired shape of the molded product, and when injecting the resin, the pressure required for conventional injection is reduced. This method eliminates the high-pressure injection used to prevent conventional "sink marks", and uses ultra-high pressure to close the microscopic gap immediately before both molds forming the cavity reach the final desired cavity shape. The purpose of this is to prevent the "sink mark" phenomenon by publishing.

The means for tightening the molds with ultra-high pressure surrounds and fixes the opposite surfaces of the male and female molds, and also covers the working surface of the mold and the entire circumference of the working surface. Using a mold that forms a gear with the inner wall of the surrounding heat receiving member and forms the end face of the heat receiving member that is connected to the inner wall as a pressure receiving surface, heating and cooling are applied only to the heat receiving member. This is repeated to cause contraction and expansion phenomena, and these phenomena are transmitted to the mold to cause reciprocating motion in the mold opening and closing directions over a short distance, and heating is applied. The material to be molded is injected into the cavity whose volume has increased due to the mold separating due to mold clamping pressure due to the contact of the pressure receiving surface of the end face of the heat receiving part that expands, and after the completion of the injection process, the heat receiving member is cooled. The effect of the two molds approaching each other due to the shrinkage phenomenon caused by cooling becomes a pressing force on the injected resin material.

Next, an embodiment of the present invention will be described with reference to the drawings. Type (1) (1
゛) and the entire surface (2+ (2) and the entire surface f
2) The inner wall (J (4) of the heat receiving member (3) (3) surrounding the entire circumference of (21) and the mold (5) (5) are molded into the cavity (6) (6) in the desired form. The end surfaces of the heat receiving member (3) (j+) connected to the inner wall (4H4) are brought into contact with each other and the surface that receives mold clamping pressure is called the pressure receiving surface (force ('
1), each of the molding molds (5) (M> ).For the mold (1) (]') of thus formed mold f5) (5), the rear end surface not having the cavity part (6) (6) is provided with a mold support frame (8). )(d) It is possible to perform the operation of closing the mold and opening the mold. This mold support frame (
8) There are two types of (8): a movable type in which only one side is movable, and a movable type in which only one side is movable.In the first illustration, the mold (1) equipped with the injection port (9) is a base (not shown). Only the mold suspension is movable, allowing mold clamping and mold opening operations. In this case, the mold (1) subjected to the suppressing action uses the mold support frame (8) to transfer the reaction force to the metal #l! (1°). The other mold (1) is designed so that the product molded in the movable recessed cavity can be taken out by opening and closing operations by operating the mold support frame (d).

However, in the present invention, the above mold support frame (8) is omitted. Reference numeral 00) in the figure is the mold opening/closing means. (1
1) is a fluid medium hole bored in the heat receiving member (3) (3'), and the fluid medium hole 0υ is connected to the heat medium supply source 0υ by a conduit 04) with an on-off valve (13) interposed. It is something that connects.

The heat receiving member (3) of the molding die (5) (5) configured as described above is provided with heating and cooling effects during resin molding.

Of this heat application process, first we will talk about heat application: heat irradiation using air as a medium, ultrasonic irradiation, radiant heat irradiation,
There are irradiation means such as flame irradiation, and means using heat exchange from a fluid heat medium such as liquid or gas, and for either method, the type of heat transfer means and the method of applying it, etc. It is not limited to. Further, the cooling means includes forced cooling means including natural cooling, and includes blowing low-temperature air, refrigerant gas, and fluids such as water. As with the heating means, these cooling means are not limited to the type of cooling means or the method of applying the cooling means. As for these heating means and cooling means, hot water and cold water, which are the most readily available and easily available, are used in the drawings, and these are shown so as to be able to flow alternately.

Next, to describe the operation of the apparatus configured as described above, an optimal temperature is applied in advance to the molds (1), (11), and the molded product during molding.
) It is desirable to have no relation to the heating and cooling in (3), and to have the heating and cooling effects not affect the mold i1) (1). Like this mold (1) (],)
When the temperature is raised to a predetermined level, a separate heating means is used to independently raise the temperature of the heat receiving member (3) (3) returning from the mold (1) (1). In this way, if both molding molds (5) <5)'e are brought close to each other and their pressure receiving surfaces (n<e) are brought into contact with each other, a cavity is formed by the cavity portion (6) f6). The volume of the cavity in this case is slightly larger than the volume of the molded product. That is, as the heat receiving member (3) (3) is heated, the heat receiving member (3) (3) undergoes a thermal expansion phenomenon from the mold (1) (1), and this expanded Heat receiving member (3) (
The distance between the entire surface (21 (2) forming the bottom of the cavity part (611 (6'l) of the mold (1) (1゛) is It is increasing.

A resin material is injected into the cavity formed by the cavity portions (6) (6), the volume of which is increasing.

At the time set after starting this injection process, the heat receiving member (3) (3
) is switched to a cooling step, and the expansion phenomenon of the heat receiving member (3) (3) shifts to the contraction phenomenon. During this work, the mold (13(1')) is operated so as to have a clamping action, so the heat receiving member (3) (,4+
The state of close contact between the pressure-receiving surfaces (force (7')) does not change in the slightest even when the expansion phenomenon changes to the contraction phenomenon; Only m(11) approaches each other to reduce the volume of the cavity, and the injected resin within the volume is compressed by a pressing force proportional to the shift to the smaller volume.

In this way, the present invention combines the cavity part (6) (6) forming part in the molding die (5+ <5) with the mold (1) (1) which is relatively unaffected by changes due to thermal expansion, and the heat of heating and cooling. Heat-receiving member (3) that expands and contracts depending on the application operation
(3) A uniform pressing force is applied to the entire molded product due to the contraction of the cavity itself, with respect to the resin once injected into the cavity. By pressurizing the product, it becomes a product with uniform density, and disadvantageous phenomena such as "sink marks" and distortion are completely eliminated, and the entire molded product becomes a molecularly uniform and well-organized product. Even if a molded article requires high optical precision, etc., it is possible to produce a molded article that can satisfy the desired conditions.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view for explaining the present invention in detail;
The figure is an enlarged schematic cross-sectional view of the main parts. II")...Mold, (2)(d)...Full surface, (31(,
3)... Heat receiving member, (4) (a)... Inner wall, (5) (
d)...Molding mold, (6) (6)...Cavity part, (force (
7)...Pressure receiving surface, 00)...Mold opening/closing means. Patent applicant Crown Industries Co., Ltd.

Claims (2)

[Claims] (1) A mold is formed by forming a mold using all four opposed surfaces of both molds forming a male and female mold, and an inner wall of a heat receiving member that surrounds and fixes the mold and surrounds the entire circumference of the entire surface of the mold. A cavity having a desired shape is formed, the end surfaces of the heat receiving member connected to the inner wall are brought into contact with each other, the surface receiving mold clamping pressure is used as a pressure receiving surface, and the pressure receiving surfaces are made to face each other to form a molding die. The heat-receiving members are brought into contact at the desired positions where they meet, and the heating and cooling actions are repeated alternately on each of these heat-receiving members, so that the heat-receiving members that receive this heat action expand due to heating and contract due to cooling. This expansion and contraction effect is transmitted to each mold, causing reciprocating motion in the mold opening and closing directions within a short distance, and the heat receiving part expands when heated. A resin material is injected into the cavity formed by the two cavity parts whose volume has increased due to the separation of the molds due to the collision of the moon, and a cooling effect is applied to the heat receiving member at the time of setting after the start of the injection process. In a mold that utilizes thermal expansion, the effect of the two molds approaching each other due to the contraction phenomenon caused by the cooling action reduces the volume of the cavity and can apply a pressing force to the entire resin within the cavity. Molding method for resin molded products. (2) The opposing surfaces of both molds forming the male and female molds, and the inner wall of the heat receiving member that surrounds and fixes the mold and surrounds the entire surface and the entire periphery of the mold as a molding mold. Form a cavity of a desired shape, bring the end surfaces of the heat receiving members that are connected to the inner wall into contact with each other, and configure each mold with the surface that receives mold clamping pressure as the pressure receiving surface, and one of the molds. Either by fixing it to the base and connecting a mold opening/closing means to the other mold, or by connecting separate mold opening/closing means to each of both molds, it can be fixed to the base and connected to the other mold. Dedication (
It is possible to apply heating and cooling only to the heat-receiving member during the contact mold clamping operation of the pressure-receiving surface, and when heating is applied, the molds are mutually connected due to the expansion phenomenon of the heat-receiving member. Molding of a resin molded product in a mold that utilizes thermal expansion, which is capable of causing a separation action between the molds and, when applying a cooling action, a shrinkage phenomenon of the heat-receiving member to bring the molds closer to each other. Device.